Technical Abstract:
The ability of LPS and CRH to elicit immune responses was compared. Brahman heifers were transported from Overton, TX, to Lubbock, TX, were fitted with jugular catheters and separated into 2 treatments groups, LPS (0.25 microgram/kg BW; n=6; 194±11 kg) or CRH (0.5 microgram/kg BW; n=6; 202±9 kg). Blood samples were collected at 0.5- or 1-hr intervals from -2 to 8 hr relative to the challenge and again at 12 and 24 hr post-challenge to determine white blood cell (WBC) and haptoglobin concentrations. Blood was collected at 0, 1, 2, 4, 6, and 24 hr post-challenge to measure phagocytic and oxidative burst capacities against an E. coli. Data were analyzed using the mixed procedure of SAS specific for repeated measures with treatment, time, and their interaction included as fixed effects. In response to challenge, WBC concentrations (9.7±0.6 million and 8.1±0.6 million cells/mL for CRH and LPS, respectively at time 0) decreased at 1 hr for both CRH- (7.2±0.6 million cells/mL) and LPS-treated heifers (1.9±0.6 million cells/mL; P<0.05), and WBC concentrations remained suppressed until 24 hr in the LPS-treated heifers. The percentage of neutrophils (N) and lymphocytes (L), and the N:L ratio did not change in response to CRH (P<0.05). Percent N and the N:L ratio initially decreased (1 to 4 hr; P<0.05) in response to LPS before increasing above baseline values (7 to 8, and 24 hr; P<0.05). Percent L increased (1 to 4 hr; P<0.05) before decreasing (7 to 8 hr; P<0.05) in response to LPS. The percentage of N phagocytizing and producing an oxidative burst increased in response to LPS (P<0.01), but decreased following the CRH challenge (P<0.01). Haptoglobin concentrations peaked 24 hr post-LPS (P<0.01; 1.9±0.2, 450 nm abs x 100) and 0.5 hr post-CRH, although the response was transient and quickly returned to baseline values (P<0.01; 3.1±0.2, 420 nm abs x 100). These data indicate that acute stress can stimulate indices normally associated with the pro-inflammatory immune response. The data imply that assessing the immunological status of an animal via one time point may not be an accurate depiction of the animal’s overall health as it may reflect a response associated with handling.